This is a phase II, multicenter, two-arm, randomized, open-label trial with a sample size of 25 patients per treatment arm. A total of 50 patients will be enrolled. The primary objectives are to assess the tolerance and safety of orally administered SQV-SGC given in combination with two NRTIs, or orally administered SQV-SGC and nelfinavir and one or two NRTIs, in HIV-infected children. The secondary objectives of this trial are as follows: 1) To assess the steady-state pharmacokinetic characteristics of SQV-SGC and NFV when given in a twice daily combination regimen to HIV-infected children; 2) To evaluate two saquinavir-containing regimens with respect to short-term and long-term changes from baseline in plasma HIV RNA concentrations, CD4, CD4%, CD8 and CD8%; 3) To evaluate immune reconstitution reflected by lymphocyte subpopulations and function during treatment with two saquinavir-containing treatment regimens; 4) To explore possible relationships between saquinavir and nelfinavir exposure and antiviral activity.